An API Gateway is a centralized entry point that manages all incoming API requests within a distributed system, typically sitting in front of backend services or microservices. It acts as a reverse proxy that routes requests to appropriate destinations while abstracting the complexity of internal architecture from external clients. This component serves as a fundamental security control in modern application security by enforcing critical policies across all API traffic.

Beyond simple request routing, an API Gateway performs essential security functions including authentication and authorization verification, rate limiting to prevent abuse and denial-of-service attacks, input validation to protect against common vulnerabilities, and request/response transformation. It also facilitates comprehensive logging and monitoring for threat detection and auditing purposes. By centralizing these cross-cutting concerns, an API Gateway strengthens the overall security posture of applications, providing a unified defensive perimeter and policy enforcement point that maintains data integrity and system availability across all API interactions.